1. Field of the Invention
The present invention relates to wireless transmission systems, and, in particular, to such systems that can be configured to operate in different transmission modes.
2. Description of the Related Art
This section introduces aspects that may help facilitate a better understanding of the invention. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is prior art or what is not prior art.
A Butler matrix is a type of reconfigurable wireless transmission (TX) system that can be used to selectively transmit multiple input signals in different combinations via different combinations of multiple antennas. For example, a relatively simple (2×2) Butler matrix can be selectively configured in either a first TX mode, in which two input signals are independently transmitted via two antennas, or a second TX mode, in which the two input signals are combined for transmission via one of the two antennas. In a Butler matrix, the relative phase difference between the two input signals determines whether the two input signals will be transmitted in the first TX mode or the second TX mode.
In some transmission applications, such as those where the two input signals are to be independently transmitted in the first TX mode at two different frequencies, the isolation requirement between the two antennas is greater than can be achieved using a conventional Butler matrix.